JWST's Science Performance (2023): Better Than Expected

Jane Rigby and colleagues reported in 2023 how the James Webb Space Telescope actually performed during its six-month commissioning. Almost across the board, Webb beat pre-launch expectations, going deeper faster than predicted, and an accurate launch left enough propellant for more than 20 years of operations.

What was JWST built to do, and could it?

JWST was designed to observe everything from near-Earth asteroids to the most distant galaxies, in infrared light. It launched on 25 December 2021 and unfolded in space, then had to be aligned, cooled and tested before any science could begin. Predictions made on the ground are only predictions. The question this paper answers is the one every user of the telescope needed settled: what can Webb really do, instrument by instrument, compared with what was promised?

What the paper found

• Better than expected. Almost across the board, science performance beat pre-launch expectations. In most cases, JWST goes deeper faster than predicted, meaning it reaches faint targets in less observing time.
• Fuel for decades. An accurate launch and efficient course corrections left enough propellant for more than 20 years of operations.
• Every instrument measured. The paper characterizes sensitivity, image quality, stability and spectral range for all four science instruments: NIRCam, NIRSpec, MIRI and FGS/NIRISS.
• Ready for its goals. Commissioning showed the observatory is fully capable of the discoveries it was built for.

How they did it

Commissioning took six months after launch. Webb sits near the Sun-Earth L2 point, about 1.5 million kilometers from Earth, behind a five-layer sunshield that keeps it cold enough to see faint infrared light. Its 6.5-meter primary mirror is made of 18 gold-coated beryllium hexagons that had to be aligned to act as a single surface.

The team then put the whole system through its paces. Sensitivity measures how faint an object the telescope can detect in a given time. Image quality measures how sharp its pictures are. Stability measures whether the pointing and focus hold steady during long exposures. The paper compares each measurement with the pre-launch predictions and reports the differences.

Why it mattered

This is the reference document for what JWST can do, and it has about 340 citations in Semantic Scholar (October 2026). Every Webb result in this library depends on the performance it documents: the 2022 detection of carbon dioxide on WASP-39b, the candidate massive galaxies found 600 million years after the Big Bang, and JADES-GS-z14-0, confirmed at redshift 14.32.

What we know now

As of October 2026, the James Webb Space Telescope is still in full operation. Cycle 5 observations began on 1 July 2026, after a record 2,930 proposals asked for time. The distance record has moved past JADES-GS-z14-0: the most distant confirmed galaxy is now MoM-z14, at redshift 14.44, seen about 280 million years after the Big Bang. For the highlights so far, see our guide to JWST’s biggest discoveries and how it compares in JWST vs Hubble.

Who wrote it

Jane Rigby led the paper with Marshall Perrin, Michael McElwain and a large team that ran commissioning. It was first posted to arXiv in July 2022 and published in the journal in April 2023.

Read the original

Rigby, J., Perrin, M., McElwain, M., et al. (2023). “The Science Performance of JWST as Characterized in Commissioning.” Publications of the Astronomical Society of the Pacific 135, 048001. doi:10.1088/1538-3873/acb293

Free to read: arXiv preprint.